This invention relates to batteries and has particular reference to lead acid batteries.
Lead acid battery technology is well established and current battery technology appears to have reached a plateau in its development. The conventional lead acid battery is formed from a series of cells, each cell having a negative and a positive electrode. The electrodes are formed of lead and have a series of plates which are positioned alternately in the cell, each plate being spaced from its neighbours by a series of separators. The plates have on their surfaces negative or positive paste which is the active component of the battery. As the paste is only poorly adherent to the lead plates, it is normally held in the interstices of a lead grid, and this means a large area of plate is necessary to obtain a reasonable number of ampere hours life from the cell. The cycle of charge and discharge tends to weaken the adherence of the paste to the plate and this permits some of the paste to fall from the plate into the bottom of the battery. To prevent the material falling from the plates building up in the bottom of the battery to an extent that it touches both plates, and shorts out the battery, a well is provided at the bottom of the cell.
The lead is conventionally used because of its fairly good resistance to corrosion by the electrolyte, but it has the major disadvantage of being very heavy. The lead is also mechanically weak and it has not proved practical to have bipolar cells using lead electrodes. In a bipolar cell, a single electrode would form the wall between adjacent cells, one face of the electrode being a negative electrode for one cell and the other face being a positive electrode for the other cell. Such an arrangement leads to weight reductions by virtue of the omission of cell walls, volume reductions by virtue of the omission of the cell walls and to improved electrical efficiency as a result of the evening out of potential across the surface of the electrodes and shortening of the electrical connecting path from one cell to the next.
In U.S. Pat. No. 3,795,543, there is described lead acid storage battery which is stated to be bipolar. In fact, however, the battery is really a mono-polar battery since a true bipolar battery has a single electrode which is positive on one side and negative on the other. In the above-mentioned US Patent, the electrodes are in fact only positive electrodes or negative electrodes although they are very close together. The present invention is concerned with truly bipolar lead acid storage batteries in which the electrodes between the cells are negative on one side and positive on the other side.